1. Field of the Invention
This invention generally relates to the construction of strings for musical instruments and more specifically to a construction and method for the manufacture of wound bass strings used in pianos.
2. Description of Related Art
Strings for musical instruments have various constructions and this invention is particularly adapted for wound strings used for the bass notes in a piano. Such strings generally comprise a steel core wire with a helical overwinding of copper wire in one, two or three layers to form single-, double- and triple-wound bass strings. A basic approach for constructing strings of this type is well known in the art. For example, Samuel Wolfendon, "A Treatise on the Art of Pianoforte Construction", Unwin Bros Ltd, Old Woking, Surrey, England, 1975, (31-33) discloses the process for achieving correct tension and loudness for different strings using such wrapping wires. The final string is stretched between the agraffe and tuning pins at the tuning block end of the piano and bridge pins and hitch pin at the other end of the piano. When tensioned and struck by a hammer, the string vibrates and
Various constructions have been proposed for piano strings. For example, U.S. Pat. No. 2,049,769 (1936) to Gray discloses wound strings for musical instruments. In this particular approach, a fabric impregnated with a suitable varnish-like material surrounds the string and fills all voids and interstices to produce a unitary string body. This composite string then owes its resonance and musical property to the structure as a whole and does not depend upon modification or muting of any reinforcement by the covering.
U.S. Pat. No. 2,746,335 (1956) to Johnson discloses a piano string in which a portion contains concentric windings. This structure discloses a double wound bass string in which the overwrapped coil or wrapping wire terminates in a flattened tapered portion.
U.S. Pat. No. 5,535,658 (1996) to Kalosdian discloses a musical instrument string with a plurality of inner wrapped wires that are helically wound about a central portion of the core wire. An outer wrapped wire is helically wound concentrically about the complete length of the inner wrapped wires and most of the side portions of the core wire. Opposite ends of the core wire extend outwardly from the outer wrapped wire. The outer wrapped wire contains the inner wrapped wires in place on the central portion of the core wire so the inner wrapped wires cannot loosen and will last longer.
Other efforts have been undertaken to control tone quality for musical strings. For example, U.S. Pat. No. 4,135,429 (1979) to Heyne discloses a piano bass string with a load carrying or core wire. At least one wrapping wire encircles the load carrying wire. The encircling, or wrapping, wire comprises a tubular casing of drawable material and a core which is heavier than the drawable material. The modulus of elasticity influences the timbre of the core and the timbre can be influenced by different proportions of copper and lead.
U.S. Pat. No. 3,523,480 (1970) to Conklin and U.S. Pat. No. 4,005,038 (1977) to Conklin disclose a different approach in which the strings for a musical instrument are tuned for both flexure and longitudinal modes of string vibration. The instrument and its strings are designed so that the frequencies of the fundamental longitudinal modes bear a specific relationship to the frequencies of the fundamental flexure modes of the string vibration. Moreover these references disclose an apparatus for wrapping the strings that comprises an elongated track mounting an opposing pair of heads having rotatable shafts to which the opposite ends of a core wire are fastened. The shafts rotate in unison. The wrapping wire is fed into contact with the core wire, maintained in tension, by a vertically disposed feed arm suspended from an overhead carriage. A predetermined tension is applied to the wrapping wire.
All of these references disclose the addition of a copper or other wrapping wire to bass strings. These additions solve loudness and space problems for bass notes, but still create a problem in tone quality. Specifically it is known that an excessively short bass strings have very poor tone quality. It has been thought that the only remedy is to lengthen the piano.
It has been found, however, that excessive inharmonicity is a fundamental contributor to poor tone quality. Derived formulas for the inharmonicity demonstrate that the unwrapped ends of wound strings contribute the most to bass string inharmonicity and become the largest contributor to poor sound tone quality. Albert Sanderson, Piano Technology Topics, 1982. In addition, there are now available and in use, instruments that assist in tuning musical instruments and establish tuning frequencies for each note in a piano. U.S. Pat. Nos. 3,968,719 and 5,285,711, assigned to the assignee of this invention, disclose, such instruments and tuning methods. Measurements in a selected number of strings produce a characteristic inharmonicity for the instrument and each string is assumed to have that inharmonicity. Conventional wound strings, however, can exhibit inharmonicity values that deviate significantly from the characteristic inharmonicity, particularly for short strings found in spinet, upright and small grand pianos. While tuning according to such methodologies as described in the foregoing references improves tuning quality, the results may still not provide an optimal tuning for the wound strings. Thus, it is important and highly desirable to provide strings that have an ideal inharmonicity.
Reducing the diameter of the core wire can modify inharmonicity, but there are undesirable effects. Reducing the diameter obviously weakens the bass strings that tend to break under constant playing. Moreover, it has been found that the inharmonicity that bare ends provide are not exactly the same as the type of inharmonicity that a core wire creates. The overtones of the bare end type of inharmonicity do not correspond exactly in frequency to those of the core wire inharmonicity except to the first approximation for low numbered overtones and various short bare end lengths.
Another approach to correcting the inharmonicity added by bare ends is to keep the bare ends as short as possible. To a first approximation, the inharmonicity contributed by bare ends rises as the cube of the length of the bare end. Customarily bare ends have been specified to be about 40 mm. This led to high inharmonicity and very poor tone quality in short scale pianos such as upright, spinet and small grand pianos. Over the years the best practice has evolved to require a bare length of less than about half that distance. This reduces the contribution of the bare ends by a factor of about 8. Even so the contribution of the bare ends to the overall inharmonicity is still too great for optimal tone quality.
Notwithstanding these advances, the issue of the contribution to inharmonicity of the bare ends of a bass string, whether single-, double- or triple-wound string, have an adverse effect particularly on short strings used in upright pianos and small grand pianos. Consequently the tone quality from such pianos often times is very poor.